Semiconductor memory device using only single-channel transistor to apply voltage to selected word line

ABSTRACT

A semiconductor memory device has a memory cell array, a first transistor of a first conductivity type, a second transistor of a second conductivity type and a third transistor of the first conductivity type. A source or drain of the first transistor is connected to each of word lines. A drain of the second transistor is connected to a gate of the first transistor. A source of the third transistor is connected to the gate of the first transistor. The gates of the second transistor and the third transistor are not connected, a source of the second transistor is not connected to a drain of the third transistor, and the gate of the second transistor and the drain of the third transistor have different voltage levels corresponding to opposite logic levels each other.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.11/858,648, filed Sep. 20, 2007, which is a continuation of prior U.S.application Ser. No. 11/374,045, filed Mar. 14, 2006 (now U.S. Pat. No.7,286,402, issued Oct. 23, 2007), which is a continuation of prior U.S.application Ser. No. 11/115,364, filed Apr. 27, 2005 (now U.S. Pat. No.7,085,162, issued Aug. 1, 2006), which is a continuation of prior U.S.application Ser. No. 10/607,153, filed Jun. 27, 2003 (now U.S. Pat. No.6,912,157, issued Jun. 28, 2005), which is a continuation of prior U.S.application Ser. No. 09/875,944, filed Jun. 8, 2001 (now U.S. Pat. No.6,621,735, Sep. 16, 2003), which is based upon and claims the benefit ofpriority from the prior Japanese Patent Applications No. 2000-173715,filed Jun. 9, 2000; and No. 2000-330972, filed Oct. 30, 2000, the entirecontents of both of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a semiconductor memory device and, moreparticularly to, a non-volatile semiconductor memory device such as aNAND cell-, NOR cell-, DINOR cell-, or AND cell-type EEPROM.

Conventionally, an electrically rewritable EEPROM is known as one of thesemiconductor memory devices. Among others, a NAND cell-type EEPROM inwhich each NAND cell block is made up of a plurality of memory cellsconnected in series is attracting attention as a device that can have ahigh degree of integration.

Each memory cell of a NAND cell-type EEPROM has a FET-MOS structure inwhich a floating gate (charge storage layer) and a control gate arestacked with an insulating film there between on a semiconductorsubstrate. A plurality of adjacent memory cells share sources and drainsand are connected in series to thereby make up a NAND cell, which isconnected to a bit line as a unit. Such NAND cells are arranged in amatrix, thus constituting a memory array. The memory array is integrallyformed in a p-type semiconductor substrate or in a p-type well.

Each drain positioned at one end of the NAND cells connected in seriesin a column direction of the memory cell array is commonly connected viaa select gate transistor to a bit line, while each source positioned atthe other end is also connected via a select gate transistor to a commonsource line. The control gates of the memory transistors and the gateelectrode of the select gate transistors are commonly connectedrespectively as a control gate line (word line) and a select gate linein the row direction of the memory cell array.

This NAND cell-type EEPROM operates as follows. Data programmingoperations mainly start from a memory cell which is the most remote fromthe bit line contact. First, when the data programming operation starts,according to write-in data, the bit line is given 0V (for “1” datawrite-in bit line) or a power supply voltage Vcc (for “0” data write-inbit line) and the select gate line on the side of a selected bit linecontact is given Vcc. In this case, in a selected NAND cell connected tothe “1” data write-in bit line, its channel portion is fixed to 0V byway of a select gate transistor. In a selected NAND cell connected tothe “0” data write-in bit line, on the other hand, its channel portionis charged via the select gate transistor up to [Vcc−Vtsg] (where Vtsgis a threshold voltage of the select gate transistor) and then enters afloating state. Subsequently, one control gate line in the selectedmemory cell in the selected NAND cell changes in potential from 0V toVpp (=20V or so, which is a programming high voltage), while the othercontrol gate line in the selected NAND cell changes in potential from 0Vto Vmg (=10V or so, which is an intermediate voltage).

Since a selected NAND cell connected to the “1” data write-in bit linehas its channel portion fixed at 0V, it has a large potential difference(=20V or so) between its selected memory cell's control gate line (=Vpppotential) and its channel portion (=0V), thus causing electrons to beinjected from the channel portion to the floating gate. Accordingly, thethreshold voltage of that selected memory cell shifts to the positivedirection, thus completing write-in of data “1”.

A selected NAND cell connected to the “0” data write-in bit line, on theother hand, has its channel portion in a floating state, so that aninfluence of capacitive coupling between its control gate line and itschannel portion raises a voltage of the control gate line (0V·Vpp, Vmg),which in turn raises a potential of the channel portion from a[Vcc−Vtsg] potential to Vmch (=8V or so) with that channel portion asheld in the floating state. In this case, since a potential differencebetween the control gate line (=Vpp potential) and the channel portion(=Vmch) of the selected memory cell in the selected NAND cell is arelatively low value of 12V or so, thus electron injection is avoided.Therefore, the threshold voltage of the selected memory cell is heldunchanged at a negative value.

Data erase is carried out to all of the memory cells in a selected NANDcell block. That is, 0V is applied to all the control gate lines of theselected NAND cell block, while a high voltage of 20V or so is appliedto the bit lines, the source lines, the p-type well regions (or p-typesemiconductor substrate), and the control gate lines and all the selectgate lines in the non-selected NAND cell blocks. Thus, in all the memorycells in the selected NAND cell block, the electrons in the floatinggate are emitted to the p-type well (or the p-type semiconductorsubstrate), thus shifting the threshold voltage to the negativedirection.

Data read-out, on the other hand, is carried out by applying 0V to thecontrol gate line of a selected memory cell and a read-out intermediatevoltage Vread (4V or so) to the control gate line and the select gateline of the other memory cells to thereby detect whether a current flowsthrough that selected memory cell.

As may be obvious from the above description, to write data into a NANDcell-type EEPROM, it is necessary to apply voltages higher than thepower supply voltage, i.e. Vpp (20V or so) to a selected control gateline in a selected block and Vmg (10V or so) to a non-selected controlgate line in that selected block.

To apply the above-mentioned voltages Vpp and Vmg, in a row decodercircuit, the current paths of two kinds of elements of an NMOStransistor (n-channel type MOS transistor) and a PMOS transistor(p-channel type MOS transistor) having different polarities areconnected in parallel to the control gate line to conduct control sothat both transistors may be turned ON and OFF in a selected block andin a non-selected block respectively.

FIG. 1 is a circuit diagram for showing a configuration example of partof the row decoder circuit in such a conventional semiconductor memorydevice.

In the circuit shown in FIG. 1, connected to each control gate line areone NMOS transistor (Qn1 to Qn8)+one PMOS transistor (Qp1 to Qp8). Thosetransistors Qn1 to Qn8 and Qp1 to Qp8 are supplied with complementarycontrol signals from nodes N1 and N2 respectively.

For data write-in, the power supply node VPPRW and a selected controlgate line have the same level in voltage like power supply nodeVPPRW=[selected control gate line voltage]=20V. In this case, connectedto each control gate line are one NMOS transistor+one PMOS transistor,so that 20V can be applied to the control gate line even when the powersupply node VPPRW is 20V. Accordingly, it is not necessary to raise thepower supply node VPPRW to (20V+Vtn) in order to apply both voltages of0V and Vpp in a selected block.

Note here that in the circuit shown in FIG. 1, memory cells M1 to M8have their current paths connected in series, thus making up one NANDcell. One end of the each NAND cell is connected via the current path ofthe select gate transistor S1 to the bit lines BL1 to BLm and the otherend, via the current path of the select gate transistor S2 to the sourceline (Cell-Source) commonly. The control gate lines CG(1) to CG(8) arecommonly connected to the control gates of the memory cells M1 to M8respectively in each NAND cell, while the select gate lines SG(1) andSG(2) are commonly connected to the gates of the select gate transistorsS1 and S2 respectively. The signal input nodes CGD1 to CGD8, SGD, SGS,and SGDS are each supplied with a decode signal. Moreover, the rowdecoder activating signal RDEC is at Vcc during general dataprogramming, read-out, and erase and at 0V during non-operation. Theblock address signal RA1, RA2, and RA3 are all at Vcc in a selectedblock and at least one of them is at 0V in the non-selected blocks.

All the PMOS transistors arranged in a region HV indicated by a brokenline in the figure are formed in the n-well region to which theprogramming high voltage Vpp is applied, so that either of the nodes N1and N2 is always at Vpp during write-in. Furthermore, the node SGDS isat 0V during write-in.

By the above-mentioned configuration, however, each of the control gatelines CG(1) to CG(8) requires two transistors Qp1 to Qp8, Qn1 to Qn8 tothereby increase the number of elements hence a pattern occupied area inthe row decoder circuit, thus problematically raising the chip cost.

To prevent an increase in the number of the elements in the row decodercircuit, on the other hand, such a circuit as shown in FIG. 2 may beused in which one transistor (e.g., only NMOS transistor QN1 to QN8) isconnected to each control gate line. The circuit shown in FIG. 2 hasalmost the same configuration of a memory block 2 as that of FIG. 1 butis different therefrom in the circuit configuration of parts 5 a and 5 bof the row decoder circuit (control gate lines CG(1) to CG(8) and atransistor portion for applying voltages to the select gate transistorsS1 and S2 and in that a pump circuit PUMP is provided.

In a case of this circuit configuration, to apply the programming highvoltage Vpp to the control gate lines CG(1) to CG(8), it is necessary toapply [VPP+Vtn] to the gates of the NMOS transistors QN1 to QN8connected to these control gate lines CG(1) to CG(8), where Vtn is athreshold voltage of the NMOS transistors QN1 to QN8 connected to thecontrol gate lines CG(1) to CG(8). Therefore, the pump circuit PUMP isprovided in the row decoder circuit.

This pump circuit PUMP comprises capacitors C1 and C2, NMOS transistorsQN21 to QN23, an inverter 6, a NAND gate 7, and depletion-type NMOStransistors QN24 and QN25.

In the circuit shown in FIG. 2, a signal OSCRD acts as an oscillationsignal during data write-in and read-out, so that a voltage raised inthe pump circuit PUMP is output to a node N1 and applied along thecurrent paths of the transistors QN1 to QN8 to the control gate linesCG(1) to CG(8). A signal TRAN is constantly set at 0V.

The above-mentioned pump circuit PUMP has the plurality of capacitors C1and C2 and so has a large area. Those two capacitors C1 and C2, inparticular, usually occupy a larger pattern area than any otherelements, thus leading to a problem that the pattern area of the rowdecoder circuit cannot sufficiently be reduced although the number ofthe transistors required for applying voltage can be decreased.

Thus, the conventional NAND cell-type EEPROM needs to provide a functionfor sending a high voltage to the word lines to thus require a pluralityof transistors to each word line in the row decoder circuit. This leadsto a problem of an increase in the pattern area of the row decodercircuit.

If, to solve this problem, one transistor is connected to each word linein the row decoder circuit, the row decoder circuit needs to have a pumpcircuit therein, a large pattern area of which pump circuit stillincreases the pattern area of the row decoder circuit.

Further, if the row decoder has one transistor connected to each wordline and has no pump circuit therein, the programming high voltagecannot be applied to the word lines without a drop in potential, thusgiving rise to a risk that data may not securely written in.

BRIEF SUMMARY OF THE INVENTION

According to an aspect of the present invention, there is provided asemiconductor memory device comprising a semiconductor memory devicecomprising:

a memory cell array in which memory cells are arranged in a matrixincluding a plurality of word lines;a first transistor of a first conductivity type, a source or drain ofthe first transistor being connected to each of the word lines;a second transistor of a second conductivity type, opposite to the firstconductivity type, a drain of the second transistor being connected to agate of the first transistor; anda third transistor of the first conductivity type, a source of the thirdtransistor being connected to the gate of the first transistor,wherein gates of the second transistor and the third transistor are notconnected, a source of the second transistor is not connected to a drainof the third transistor, and the gate of the second transistor and thedrain of the third transistor have different voltage levelscorresponding to opposite logic levels each other.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a circuit diagram for showing a configuration example of a rowdecoder circuit and part of a memory cell array in a conventionalsemiconductor memory device;

FIG. 2 is a circuit diagram for showing another configuration example ofthe row decoder circuit and part of the memory cell array in theconventional semiconductor memory device;

FIG. 3 is a block diagram for showing a schematic configuration of aNAND cell-type EEPROM, intended to explain a semiconductor memory deviceaccording to an embodiment of the present invention;

FIG. 4A is a plan view for showing a pattern of one NAND cell portion inthe memory cell array of FIG. 3;

FIG. 4B is an equivalent circuit diagram for showing the one NAND cellportion of the memory cell array of FIG. 3;

FIG. 5A is a cross-sectional view taken along line 5A-5A of FIG. 4;

FIG. 5B is a cross-sectional view taken along line 5B-5B of FIG. 4;

FIG. 6 is an equivalent circuit diagram of a memory cell array in whichthe AND cell is arranged in a matrix;

FIG. 7 is a circuit diagram for showing a configuration example of a rowdecoder circuit and part of a memory cell array in a semiconductormemory device according to a first embodiment of the present invention;

FIG. 8 is a timing chart for showing a data programming operation in thesemiconductor memory device according to the first embodiment of thepresent invention;

FIG. 9 is a timing chart for showing a data read-out operation in thesemiconductor memory device according to the first embodiment of thepresent invention;

FIG. 10 is a timing chart for showing a data erase operation in thesemiconductor memory device according to the first embodiment of thepresent invention;

FIG. 11 is a circuit diagram for showing a configuration of a rowdecoder circuit and part of a memory cell array in a semiconductormemory device according to a second embodiment of the present invention;

FIGS. 12A and 12B are illustrations for explaining a shape of an n-wellregion in the row decoder circuit in the semiconductor memory devicesaccording respectively to the first and second embodiments of thepresent invention;

FIG. 13 is a circuit diagram for showing a configuration example of arow decoder and part of a memory cell array in a semiconductor memorydevice according to a third embodiment of the present invention;

FIG. 14 is a circuit diagram for showing a configuration example of arow decoder and part of a memory cell array in a semiconductor memorydevice according to a fourth embodiment of the present invention;

FIG. 15 is an illustration for showing a first block arrangement exampleof the memory cell array and the row decoder circuit in thesemiconductor memory device according to the embodiment of the presentinvention;

FIG. 16 is an illustration for showing a second block arrangementexample for the memory cell array and the row decoder circuit in thesemiconductor memory device according to the embodiment of the presentinvention;

FIG. 17 is an illustration for showing a third block arrangement examplefor the memory cell array and the row decoder circuit in thesemiconductor memory device according to the embodiment of the presentinvention;

FIG. 18 is an illustration for showing a first example of the blockarrangement of the memory cell array and the row decoder and the shapeof the n-well region in the semiconductor memory device according to theembodiment of the present invention;

FIG. 19 is an illustration for showing a second example of the blockarrangement of the memory cell array and the row decoder and the shapeof the n-well region in the semiconductor memory device according to theembodiment of the present invention;

FIG. 20 is an illustration for showing a third example of the blockarrangement of the memory cell array and the row decoder and the shapeof the n-well region in the semiconductor memory device according to theembodiment of the present invention;

FIGS. 21A to 21E are illustrations for explaining the row decodercircuit block arrangement and the n-well region shape in thesemiconductor devices according to the first through fourth embodimentsand many other embodiments of the present invention;

FIG. 22 shows circuit diagrams for illustrating a first configuration ofthe row decoder circuit in the block address decoder portion and thevoltage switching circuit in the semiconductor devices according to thefirst through fourth embodiments and many other embodiments of thepresent invention;

FIG. 23 shows circuit diagrams for illustrating a second configurationof the row decoder circuit in the block address decoder portion and thevoltage switching circuit in the semiconductor devices according to thefirst through fourth embodiments and many other embodiments of thepresent invention;

FIG. 24 shows circuit diagrams for illustrating a third configuration ofthe row decoder circuit in the block address decoder portion and thevoltage switching circuit in the semiconductor devices according to thefirst through fourth embodiments and many other embodiments of thepresent invention;

FIG. 25 shows circuit diagrams for illustrating a fourth configurationof the row decoder circuit in the block address decoder portion and thevoltage switching circuit in the semiconductor devices according to thefirst through fourth embodiments and many other embodiments of thepresent invention;

FIG. 26 is an illustration for explaining the row decoder circuit blockarrangement and the n-well region shape in the semiconductor memorydevice according to many other embodiments;

FIG. 27 is an illustration for explaining the row decoder circuit blockarrangement and the n-well region shape in the semiconductor memorydevice according to many other embodiments;

FIG. 28 is an illustration for explaining the row decoder circuit blockarrangement and the n-well region shape in the semiconductor memorydevice according to many other embodiments;

FIGS. 29A and 29B are illustrations for explaining the row decodercircuit block arrangement and the n-well region shape in thesemiconductor memory device according to many other embodiments;

FIG. 30 is a circuit diagram for showing another configuration exampleof the row decoder circuit in the semiconductor memory device accordingto a fifth embodiment of the present invention;

FIGS. 31A to 31D are circuit diagrams for showing specific configurationexamples of the voltage switching circuit in the circuit shown in FIG.30;

FIG. 32 is a circuit diagram for showing another configuration exampleof the row decoder in the semiconductor memory device according to asixth embodiment of the present invention;

FIGS. 33A to 33D are circuit diagrams for showing specific configurationexamples of the voltage switching circuit in the circuit shown in FIG.32;

FIG. 34 is a circuit diagram for showing an extracted circuit portionfor supplying a high voltage to the voltage switching circuit in theabove-mentioned embodiments, intended to explain the semiconductormemory device according to another embodiment;

FIG. 35 is a circuit diagram for showing an extracted circuit portionfor supplying a high voltage to the voltage switching circuit in theabove-mentioned embodiments, intended to explain the semiconductormemory device according to further another embodiment;

FIG. 36 is an equivalent circuit diagram for showing a memory cell arrayin a NOR cell-type EEPROM;

FIG. 37 is an equivalent circuit diagram for showing a memory cell arrayin a DINOR cell-type EEPROM;

FIG. 38 is an equivalent circuit diagram for showing a memory cell arrayin an AND cell-type EEPROM; and

FIG. 39 is an equivalent circuit diagram for showing a memory cell arrayin a NOR cell-type EEPROM provided with a selection transistor.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 is a block diagram for showing a schematic configuration of aNAND cell-type EEPROM, intended to explain a semiconductor memory deviceaccording to an embodiment of the present invention. To a memory cellarray 101 is connected a bit line control circuit (sense-amplifier/datalatch) 102 for data write-in, read-out, re-write-in, and verifyread-out. This bit line control circuit 102 is connected to a datainput/output buffer 106 to thereby receive as an input an output of acolumn decoder 103 for receiving an address signal from an addressbuffer 104.

Furthermore, to the above-mentioned memory cell array 101 is connected asubstrate potential control circuit 107 for controlling a potential of ap-type silicon substrate (or p-type well region) in which this memorycell array 101 is formed. In addition, a programming high voltagegenerating circuit 109 and a programming intermediate voltage generatingcircuit 110 are provided for generating the programming high voltage Vpp(20V or so) and the intermediate voltage Vmg (10V or so) respectivelyduring a data programming operation. Further, a read-out intermediategenerating circuit 111 is provided for generating the read-outintermediate voltage Vread during a data read-out operation. Moreover,an erasing high voltage generating circuit 112 is provided forgenerating the erase high voltage Vpp (20V or so) during an eraseoperation.

The bit line control circuit 102 is mainly made up of CMOS flip-flops,thus carrying out a sense operation for latching write-in data orreading a bit line potential, a sense operation for verify reading aftera programming operation, and latching re-write-in data.

FIGS. 4A and 4B are a pattern plan view and an equivalent circuitdiagram respectively of one NAND cell portion in the above-mentionedmemory cell array 101 and FIGS. 5A and 5B are cross-sectional viewstaken along lines 5A-5A and 5B-5B respectively of FIG. 4. On a p-typesilicon substrate (or p-type well region) surrounded by an elementisolating oxide film 12 is formed the memory cell array comprised of aplurality of NAND cells. As can be seen from a look at one of those NANDcells, in this embodiment, eight memory cells M1 to M8 are connected inseries to thereby make up one NAND cell.

In configuration, in the memory cells M1 to M8 are formed via a gateinsulating film 13 on the substrate 11 floating gates 14 (141, 142, . .. , 148), on which are formed via an insulating film 15 control gates 16(word lines of 161, 162, . . . , 168). The n-type diffusion layers 19(190, 192, . . . , 1910) which provide sources and drains of thosememory cells are connected in such a manner that adjacent paired ones ofthem may be shared in use as a source or a drain.

On the drain and source sides of the NAND cell are respectively formed apair of select gates 149 and 169 and a pair of select gates 1410 and1610 simultaneously with the memory cell floating gates and the controlgates. The substrate 11 on which the elements are formed is covered by aCVD oxide film 17, on which a bit line 18 is provided. The bit line 18is in contact with a drain-side diffusion layer 19 at one end of theNAND cell. Control gates 16 for the NAND cells arranged in rows areprovided commonly as gate lines CG (1), CG(2), . . . , CG(8). Thosecontrol gates provide word lines. The select gate pair of 149 and 169and that of 1410 and 1610 are also sequentially provided as select gatesSG(1) and SG(2) respectively in a row direction.

FIG. 6 shows an equivalent circuit diagram of the memory cell array inwhich such NAND cells are arranged in a matrix. A group of the NANDcells sharing the same word line or select line is called a block and,for example, a region surrounded by a broken line in FIG. 6 is definedas one block. During a usual read-out or programming operation, only oneof a plurality of those blocks is selected, which is called a selectedblock.

FIG. 7 shows a configuration example of a row decoder circuit and partof the memory cell array in a semiconductor memory device according tothe first embodiment of the present invention. In the configurationshown in FIG. 7, the elements in one block size of circuit is arrangedon both sides of a memory cell block 2. The circuit shown in FIG. 7features that transistors QN0 to QN10 connected to the control gatesCG(1) to CG(8) and the select gates SG(1) and SG(2) are all of then-channel type, that transistors QN1 to QN8 connected to the controlgates CG(1) to CG(8) are provided one for each control gate line, andthat PMOS transistors QP11 and QP12 are provided between an output nodeN1 and a power supply node VPPRW of a voltage switching circuit 54A forsetting a gate voltage of the transistors QN0 to QN10 connected to thecontrol gate CG(1) to CG(8) or the selected gate lines SG(1) and SG(2).

That is, between the control gates CG(1) to CG(8) and the signal inputnodes CGD1 to CGD8 are connected current paths of the NMOS transistorsQN1 to QN8 respectively. Furthermore, between the select gate line SG(1)and the signal input nodes SGD and SGDS are connected current paths ofthe NMOS transistors QN0 and QN9 respectively. Further, between theselect gate line SG(2) and the signal input node SGS is connected acurrent path of the NMOS transistor QN10.

The above-mentioned voltage switching circuit 54A comprises PMOStransistors QP11 and QP12, NMOS transistors QN11 and QN12, and aninverter 55. The PMOS transistors QP11 and QP12, and NMOS transistorsQN11 and QN12 are connected so as to act as a flip-flop 56, while oneend of each of the current paths of the PMOS transistors QP11 and QP12and the back gate are commonly connected to one power supply node VPPRW.The current paths of the NMOS transistors QN11 and QN12 are connectedbetween the other end of each of the current paths of the PMOStransistors QP11 and QP12 and the other power supply node, e.g. a groundpoint. The gate of the PMOS transistor QP11 is connected to the otherend of the current path of the PMOS transistor QP12 and a node N1, whilethe gate of the PMOS transistor QP12 is connected to the other end ofthe current path of the PMOS transistor QP11. The output terminal of theinverter 55 is connected to the gate of the NMOS transistor QN12 and theinput terminal, to the gate of the NMOS transistor QN11.

The first input terminal of a NAND gate 57 is supplied with a signalRDEC and the second through fourth inputs, with signals RA1, RA2, andRA3 respectively. To the output terminal of this NAND gate 57 areconnected an input terminal of an inverter 58 and a node N2. To anoutput terminal (node N0) of the inverter 58 are connected an inputterminal of the inverter 55 and the gate of the NMOS transistor QN11.

Note here that the signal RDEC in FIG. 7 is a row decoder activatingsignal and generally at Vcc during a data programming, read-out, anderase operations and at 0V during non-operation. In addition, thesignals RA1, RA2, and RA3 are respective block address signals and areall at Vcc in a selected block and at least one of them is at 0V in anon-selected block. Therefore, the node N0 is at Vcc only in a selectedblock during operation and always at 0V during non-operation or in anon-selected block.

FIGS. 8 to 10 show shows timing charts illustrating data programming,data read-out, and data erase operations by use of the circuit shown inFIG. 7 respectively. The following will describe timings for thoseoperations briefly. Although a case will be described in which thecontrol gate line CG(2) is selected of the eight control gate linesCG(1) to CG(8) in a selected block in the data programming and read-outoperations of FIGS. 8 and 9 and the subsequent, the description holdstrue also with the case where any of the other control gates isselected.

In a data programming operation shown in FIG. 8, when the operationstarts, first a row decoder in a selected block is selected to set thenodes N0 and N1 to Vcc and the node N2 to 0V. As a bit line havingwrite-in data being “0” is charged up from 0V to Vcc, SG(1) in theselected block is set to [Vcc−Vtsg]. Then, the power supply node VPPRWis changed in voltage from Vcc to (20V+Vtn) (where Vtn is a thresholdvoltage of the NMOS transistors QN1 to QN8 directly connected to thecontrol gates CG(1) to CG(8)), which in turn changes the voltage of theoutput node N1 of the voltage switching circuit 54A also from Vcc to(20V+Vtn).

When, subsequently, the signal input node CGD2 is changed from 0V to 20Vand the signal input nodes CGD1 and CGD3 to CGD8 are changed from 0V to10V in voltage, since at this point in time the voltage of the gate ofthe NMOS transistor connected to the control gate line is at (20V+Vtn),the voltage is applied without a potential drop from the signal inputnode CGDi to the control gate line CG(I), thus changing the control gateCG(2) from 0V to 20V and the control gate lines (CG(1) and CG(3) toCG(8) from 0V to 10V in voltage. At the same time, the voltage Vchannelof the channel portion of a NAND cell of the selected block connected tothe “1” write-in bit line is fixed at 0V, while the voltage Vchannel ofthe channel portion of a NAND cell in the selected block connected tothe “0” write-in bit line is raised to 8V or so due to an influence ofcapacitive coupling with the control gate line. This state is held for awhile, to cause electrons to be injected to the floating gate of amemory cell having “1” write-in data, thus carrying out a dataprogramming operation. Afterward, when the control gate lines CG(1) to(8) in the selected block are all set to 0V, the “0” data write-in bitlines and the select gate line SG(1) are set to 0V and the power supplynode VPPRW is set to Vcc. Finally, the source line (Cell-Source) is setto 0V and the nodes N0, N1, and N2 are set to 0V, 0V, and Vccrespectively, thus ending the data programming operation.

In a data read-out operation shown in FIG. 9, when the operation starts,first a row decoder in a selected block is selected and the nodes N0 andN1 are set to Vcc and the node N2, to 0V. Furthermore, a bit line fordata read-out is pre-charged to Vcc. Then, when the power supply nodeVPPRW and the node N1 are set to (4V+Vtn) and the signal input nodesCGD1 and CGD3 to CGD8 and the signal input nodes SGD and SGS are changedfrom 0V to 4V and the signal input node CGD2 is fixed at 0V in voltage,since at this point in time the gate of an NMOS transistor connected toa control gate or select gate line is supplied with an applicationvoltage higher than 4V by a threshold voltage, that application voltagecan be applied to the control line or select gate line. In this case,therefore, in the selected block, the non-selected control gate linesCG(1) and CG(3) to CG(8) and the selected gate lines SG(1) and SG(2) arechanged from 0V to 4V and the selected control gate line is fixed at 0Vin voltage. This state is held for while, thus reading out the data in aselected memory cell. Subsequently, the control gate lines CG(1) toCG(8) and the selected gate lines SG(1) and SG(2) in the selected blockare all set to 0V and also the power supply node VPPRW is changed from(4V+Vtn) to Vcc, the bit line is set to 0V and the nodes N0, N1, and N2are set to 0V, 0V, and Vcc respectively in voltage, thus ending the dataread-out operation.

In a data erase operation shown in FIG. 10, when the operation starts,first a row decoder in a selected block is selected and the nodes N0 andN1 are set to Vcc and the node N2 is set to 0V. Moreover, since thesignal input nodes SGD, SGD, and SGDS are all set to Vcc, the selectgate line SG(1) in both the selected and non-selected blocks and theselect gate line SG(2) in the selected block are all charged up to(Vcc−Vtn) and then enter a floating state. At this point in time, thecontrol gate line and the select gate line SG(2) in the non-selectedblock are all in a floating state as held at 0V or so. Subsequently,when the p-type well region (Cell-pwell) in which the memory cell arrayis formed is changed from 0V to 20V in voltage, the select gate linesSG(1) and SG(2) in both the selected and non-selected blocks and thecontrol gate line in the non-selected block in a floating state all riseto 20V or so due to an influence of capacitive coupling with the p-typewell region, thus fixing only the control line in the selected block at0V. This state is held for a while, to thereby cause electrons to beinjected to from the floating gate in a memory cell in the selectedblock to the p-type well region, thus carrying out data erase.Subsequently, when the p-type well is changed to 0V in voltage, theselect gate lines SG(1) and SG(2) in both the selected and non-selectedblocks and the control gate line in the non-selected block in a floatingstate all drop to 0V−Vcc or so due to an influence of capacitivecoupling with the p-type well region and then are fixed at 0V. Finally,the nodes N0, N1, and N2 are changed to 0V, 0V, and Vcc respectively involtage, thus ending the data erase operation.

As mentioned above, in the row decoder circuit shown in FIG. 7, during adata programming or read-out operation, by applying to the power supplynode VPPRW a voltage higher at least by Vtn (threshold voltage of thevoltage application transistors QN0 to QN10) than the highest voltageapplied to the control gate line and the select gate line, a programminghigh voltage or a read-out high voltage can be applied to the controlgate without a potential drop to thereby realize a highly reliableoperation even if only an NMOS transistor is connected to each controlgate line or select gate line.

Furthermore, by providing only one NMOS transistor connected to eachcontrol gate line, a row decoder circuit having fewer elements can berealized, to reduce its pattern area, thus decreasing the chip sizehence the chip cost.

Further, by using such a voltage switching circuit 54A for outputting a“high” level voltage via the PMOS transistors QP11 and QP12, which areopposite in conductivity type to the transistor connected to the controlgate line or the select gate line, the voltage switching circuit 54 canbe made up with fewer elements and a smaller pattern occupied area, torealize a row decoder with fewer elements and a smaller pattern occupiedarea, which in turn reduces the chip size hence the chip cost.

FIG. 11 shows a configuration example of another part of the row decodercircuit in the semiconductor memory device according to a secondembodiment of the present invention. The circuit in FIG. 11 differs fromthat of FIG. 7 in a circuit configuration of its voltage switchingcircuit 54B, in which a depletion type NMOS transistor QD1 between thepower supply node VPPRW and a pair of the transistors QP11 and QP12.Timing charts for data programming, read-out, and erase operations byuse of the circuit shown in FIG. 11 are the same as those in FIGS. 8 to10.

The following will describe advantages of providing the transistor QD1.

Since, in the circuit of FIG. 7, a potential level of the power supplynode VPPRW is directly applied to the sources of the PMOS transistorsQO11 and QP12 and the n-well region constituting these transistors, inall the blocks irrespective of whether selected or non-selected, thesources and the n-well region of the transistors QP11 and QP12 need tobe charged up to the potential level of the power supply node VPPRW.This means that the sources and the n-well regions of several hundredsto several thousands of elements should be charged up simultaneously toenlarge the capacitance of the power supply node VPPRW, because blocksare generally provided several hundreds to several thousands on eachchip. In a data programming or read-out operation, a boosted voltagesuch as (20V+Vtn) or (4V+Vtn) is applied to the power node VPPRW, sothat if the power supply node VPPRW has a larger capacitance, therewould occur such problems as an increased size of a boosted voltagegenerating circuit, a larger power dissipation, a longer time requiredfor charging of the boosted voltage, and resultant prolonged operations.

In the circuit of FIG. 11, on the other hand, since the node N0 is at“high” level (=Vcc) in a selected block, the voltage of the node N1input to the gate of the transistor QD1 is at a “high” level (=VPPRWpotential level) and the voltage of the node N3 at a potential of thesource and n-well region of the transistors QP11 and QP12 is also at a“high” level (=VPPRW potential level), thus enabling realizing theoperations of FIGS. 8 to 10 irrespective of whether the transistor QD1is provided or not. Since the node N0 is at 0V, i.e. “low” level, in anon-selected block when the circuit of FIG. 11 is in use, the node N1input to the gate of the transistor QD1 is fixed at 0V, so that the nodeN3 is at Vtd (where Vtd indicates the highest possible voltage,generally Vcc or lower, that can be applied via the transistor QD1 whenthe gate voltage of the transistor QD1 is equal to 0V).

Thus, by using the circuit of FIG. 11, the potential of the source andn-well region of the transistors QP11 and QP12 can be changed inselected and non-selected blocks.

The shapes of the n-well region constituting the transistors QP11 andQP12 are shown in FIGS. 12A and 12B. FIGS. 12A and 12B show examples offorming the n-well region when the circuit configurations of FIGS. 7 and11 are employed respectively. In the circuit of FIG. 7, since the n-wellvoltage is at the same potential in all the blocks, as shown in FIG.12A, such a method is employed that one n-well region NW is formed overall the blocks Block1-BlockN to form the PMOS transistors QP11 and QP12in this region.

In the circuit of FIG. 11, on the other hand, since the n-well voltageis different between the selected and non-selected blocks, as shown inFIG. 12B, such a method is effective that one n-well region NW1 to NWNis formed for each block Block1-BlockN to form the PMOS transistors QP11and QP12 in these regions NW1 to NWN. The n-well regions are thusdivided into the blocks in a one-to-one relationship to charge up only aselected n-well region to a boosted voltage (20V or 4V) higher than thepower supply voltage, thus enabling greatly decreasing the loadcapacitance of the boosted voltage. This in turn can reduce the area ofthe boosted voltage generating circuit, the power dissipation, and thetime required for charging the boosted voltage, thus speeding up theoperations.

FIG. 13 shows a configuration example of further another part of the rowdecoder circuit in the semiconductor memory device according to a thirdembodiment of the present invention. The circuit of FIG. 13 differs fromthat of FIGS. 7 and 11 in a configuration of its voltage switchingcircuit 54C. This voltage switching circuit 54C comprises depletion typeNMOS transistors QD2, a PMOS transistor QP13, and depletion type NMOStransistors QD3 and QD4. One end of a current path of the NMOStransistor QD2 is connected to the power supply node VPPRW and its gate,connected to the node N1. One end of a current path of and a back gateof the PMOS transistor QP13 are connected to the other end of thecurrent path of the NMOS transistor QD2 and the other end of the currentpath is connected to the node N1 and the gate thereof, to an outputterminal of the NAND gate 57. One end of a current path of the NMOStransistor QD3 is connected to the node N1 to apply the power supplyvoltage Vcc to its gate. One end of a current path of the NMOStransistor QD4 is connected to the other end of the current path of theNMOS transistor QD3 and the other end thereof is connected to an outputterminal of the inverter 58 to supply a signal TRAN to the gate thereof.

Operation waveforms of the circuit of FIG. 13 are the same as thoseshown in FIGS. 8 to 10 and the voltage on the node N4 in FIG. 13 is alsothe same as that on the node N3 in FIG. 11. Accordingly, like in a casewhere the circuit of FIG. 11 is used, when the circuit of FIG. 13 isalso used, the voltage on the node N4 is different between a selectedblock and a non-selected block, that is the voltage of the source andn-well region of the PMOS transistor QP13 for applying a “high” level(=boosted voltage) to the node N1 is different between the selected andnon-selected blocks. Accordingly, such an n-well configuration as shownin FIG. 12B can be used to resultantly reduce the load capacitance ofthe boosted voltage. In addition, the signal TRAN is usually used asfixed at 0V and the node N0 is also at 0V in a non-selected block, sothat 0V is applied to the Node N1 via the deletion type NMOS transistorsQD4 and QD3. Further, in a selected block, the node N0=Vcc and the nodeN1·Vcc in voltage, so that the NMOS transistor QD4 is turned OFF, tothereby hold the Node N1 at a “high” level.

The above-mentioned circuit shown in FIG. 13 has other advantages suchas a first one that it has fewer elements required to constitute thevoltage switching circuit 54C (four in FIG. 13 as against seven in FIG.11) and a second one that it has a smaller difference in potentialbetween the source, drain, and n-well regions of the PMOS transistorQP13. As for the latter advantage, when the transistor QP13 is ON,always source region=drain region=n-well region, and when it is OFF,source region=n-well region=Vtd (where Vtd is the highest value of avoltage that can be applied via the transistor QD2 when the gate voltageof the transistor QD2 is equal to 0V) and also drain region=0V involtage, so that the potential difference between the source, drain, andn-well regions is at most Vcc or so despite an operation whereby aprogramming high voltage (20V or so) is applied.

Although the above embodiment of the present invention has beendescribed with reference to a case where as shown in FIGS. 7, 11, and 13the row decoder circuit for driving the control gate line and the selectgate line in each block is arranged on both sides of the memory cellarray, the present invention is applicable also to other cases where asshown in FIG. 14, for example, the row decoder corresponding to eachblock is arranged on one side of the memory cell array. Although FIG. 14does not show any specific circuit configuration as that of the voltageswitching circuit 54D, a variety of other circuit configurations may beused such as those shown in, for example, FIGS. 7, 11, and 13.

Now, FIGS. 15 to 17 show an example of arranging the row decoder. FIG.15 shows a case where the row decoder circuit for driving the controlgate line and the select gate line in each block is arranged on bothsides of the memory cell array, corresponding to the embodiment shown inFIGS. 11 and 13. FIGS. 16 and 17 both show a case where the row decodercorresponding to each block is arranged on one side of the memory cellarray, corresponding to FIG. 14. A width (pitch) of a created pattern ofthe row decoder corresponding to one block is a length of two NAND cellswhen a configuration of FIGS. 16 and 17 is employed, which is largerthan a length of one NAND cell (length of one NAND cell in the bit linedirection) for that of FIG. 15.

FIGS. 18 to 20 show a configuration that an n-well region for forming aPMOS transistor is added to the above-mentioned configuration of FIGS.15 to 17. FIGS. 15 to 17 correspond to FIGS. 18 to 20 respectively. Asmay be obvious from FIGS. 18 to 20, the configuration shown in FIG. 14has a pitch for forming a pattern of the row decoder circuit twice thatshown in FIGS. 11 and 13, hence a double pitch of the n-well region forforming the PMOS transistor. Accordingly, the design rules can berelaxed, thus realizing a chip having higher reliability and yield.Moreover, even with the finer design rules possible in the future, theconfiguration shown in FIG. 14 has a feature that the n-well region maybe divided into a plurality of blocks more likely than that shown inFIGS. 11 and 13.

The above-mentioned n-well region may be arranged otherwise, for exampleas shown in FIGS. 21A to 21E. FIGS. 21A to 21E show the row decoderregion, specifically only those blocks adjacent in a region in which therow decoder pattern is formed.

FIG. 21A shows the configuration shown in FIGS. 18, 19, and 20 (i.e.,configuration in which that shown in FIG. 21A is applied to a blockarrangement shown in FIGS. 15 to 17), in which n-well regions NWi andNWj are formed in adjacent blocks Block-i and Block-j respectively.

FIGS. 21B, 21C, and 21D show cases where for the row decodercorresponding to each block, the n-well regions NWi and NWj are formedover a plurality of blocks Block-i and Block-j, so that if a one-blockpitch for forming the row decoder cannot accommodate the design rulesfor the surrounding of the n-well regions NWi and NWj, such aconfiguration shown in FIGS. 21B, 21C, and 21D is effective that onen-well region is formed in two blocks of a region.

In case of more stringent design rules in the future, as shown in FIG.21E, one n-well region NWi-NWl should preferably be formed in fourblocks of Block-i-Block-l or even in three or five or even more blocks,thus providing a variety of applicable configurations.

Thus, the application of the configuration of FIGS. 21B to 21E to theblock arrangement of FIGS. 15 to 17 is very effective in accommodating areduction in the design rules. In particular, since the n-well regionsuch as the above-mentioned PMOS transistors QP11, QP12, and QP13 towhich is applied a voltage (e.g., boosted voltage) higher than the powersupply voltage is difficult to reduce the design rules, enlargement inthe pitch and relaxation of the design rules have large effects.

In FIGS. 11, 12A, 12B, 13, 14, 18 to 20, and 21A to 21E, such anembodiment has been described that one n-well region for forming PMOStransistors therein is provided for each block of the row decodercircuit. The present invention, however, is effective also in a casewhere, for example, one n-well region is shared over adjacent blocks.

FIGS. 22 to 25 show a circuit configuration example of an addressdecoding portion and the voltage switching circuit portion 54 (54A, 54B,54C, and 54D) of two adjacent blocks of the row decoder circuit in acase where one n-well region is shared by adjacent blocks and also inthe case of the above-mentioned circuit. FIG. 22 corresponds to thecircuit of FIG. 11 and FIG. 23, to that of FIG. 13. FIG. 24 shows acircuit configuration example in the case where one n-well region isshared over adjacent blocks, corresponding to a configuration based onthe circuit shown in FIG. 11. FIG. 25 shows a circuit configurationexample in a case where one n-well region is shared over adjacentblocks, corresponding to a configuration based on the circuit shown inFIG. 13. FIG. 24 has no addition of elements with respect to FIG. 22,while FIG. 25 has an addition of one depletion type NMOS transistor foreach block with respect to FIG. 23.

When the circuit shown in FIGS. 24 and 25 is used, if at least one ofthe two blocks sharing the n-well region is selected, the n-well regionis set at a voltage at the time of selection (i.e., 20V+Vtn at write-in,4V+Vtn at read-out, and Vcc at erase) and otherwise, the n-well regionis set at Vtd, i.e. voltage at the time of unselection. Also in thiscase, since the n-well region to which a boosted voltage is appliedincludes a selected block, there is provided such an advantage that theload capacitance of the boosted voltage can be greatly reduced ascompared to the conventional case (which corresponds to FIG. 12A).

Although the present invention has been described with a case where inFIGS. 22 to 25, continual-address blocks of Block-i and Block-(i+1) areadjacent as the adjacent ones in the row decoder circuit region, othercases of the blocks not being of continual addresses can of course beaccommodated by the present invention as far as the n-well region isshared over the adjacent blocks in the row decoder circuit region.

FIGS. 26 to 28 show a formation example of the n-well region when thecircuit configuration shown in FIGS. 24 and 25 is used, in which onen-well region is shared over adjacent blocks in configuration. By usingthe configuration shown in FIGS. 24, 25, and 26 to 28, it is possible toenlarge the pitch for the formation of the n-well region hence relax thedesign rules of the surroundings of the n-well region as compared to thecase of using that shown in FIGS. 22, 23, and 18 to 20, thus improvingthe reliability and the yield. In particular, since the n-well regionincluding the above-mentioned PMOS transistors QP11, QP12, QP13, etc. towhich a voltage (e.g., boosted voltage higher than the power supplyvoltage) is applied is difficult to reduce the design rules, the pitchenlargement and the deign relaxation of the above-mentionedconfiguration are very effective.

Further, the configuration shown in FIGS. 24, 25, and 26 to 28 has anadvantage of decreasing the number of the n-well regions, thus reducingthe area of the pattern of the row decoder circuit. There is providedsuch a method for further relaxing the design rules shown in FIGS. 29Aand 29B that one n-well region common to two blocks is provided for thepitch of three to four blocks, which is the same concept as that ofFIGS. 21B to 21D as against FIGS. 18 to 20. This method of FIGS. 29A and29B is also very effective.

FIG. 30 shows a configuration example of another part of the row decodercircuit in the semiconductor memory device according to a fifthembodiment of the present invention. The circuit shown in FIG. 30 has anaddition of a voltage switching circuit 54E with respect to the circuitshown in FIG. 14 in configuration. That is, the NAND gate 57 has itsfirst input terminal supplied with the row-address activating signalRDEC and its second through fourth input terminals supplied with theblock address signals RA1, RA2, and RA3 respectively. At the outputterminal of this NAND gate 57 is connected an input terminal of theinverter 58, so that an output signal in1 of this inverter 58 issupplied to the voltage switching circuits 54D and 54E. To theabove-mentioned voltage switching circuit 54E is applied a voltage Vm asthe operating power supply voltage. In addition, an output signal out1of the above-mentioned voltage switching circuit 54E is applied to thevoltage switching circuit 54D. The other circuit portions are the sameas those of the circuit shown in FIG. 14 and so not detailed here,because the same elements are indicated by the same reference numerals.

FIGS. 31A to 31D are circuit diagrams for showing specific configurationexamples of the voltage switching circuit 54E in the above-mentionedcircuit shown in FIG. 30. In any of them, to the voltage switchingcircuit 54E is input the output signal in1 of the inverter 58, so thatwhen this signal in1 is at the “high” level, 0V is output and, when thesignal in1 is at the “low” level, the signal out1 of the Vm level isoutput.

A circuit shown in FIG. 31A comprises an inverter INVa, NMOS transistorsQN13 and QN14, and PMOS transistors QP14 and QP15. The output signal in1of the inverter 58 is supplied to the input terminal of the inverterINVa and the gates of the NMOS transistor QN14. To the output terminalof the inverter INVa is connected the gate of the NMOS transistor QN13.The sources of the NMOS transistors QN13 and QN14 are connected to theother power supply node, e.g. the ground point, while between theirdrains and the power supply node Vm are connected the drains and thesources of the PMOS transistors QN14 and QP15 respectively. The gate ofthe PMOS transistor QP14 is connected to the common-drain connectionpoint between the PMOS transistor QP15 and the NMOS transistor QN14,while the gate of the PMOS transistor QP15 is connected to thecommon-drain connection point between the PMOS transistor QP14 and theNMOS transistor QN13. Accordingly, the output signal out1 obtained atthe common-drain connection point between the transistors QP15 and QN14is supplied to the input terminal of the voltage switching circuit 54D.

Furthermore, a circuit shown in FIG. 31B comprises an inverter INVb,NMOS transistors QN15 and QN16, PMOS transistors QP16 and QP17, and adepletion type NMOS transistor QD5. The output signal in1 of theinverter 58 is supplied to the input terminal of the inverter INVb andthe gate of the NMOS transistor QN16. At an output terminal of theinverter INVb is connected the gate of the NMOS transistor QN15. Thesources of the NMOS transistors QN15 and QN16 are commonly connected tothe ground point and their drains are connected with the drains of thePMOS transistors QP16 and QP17 respectively. The gate of the PMOStransistor QP16 is connected to a common-drain connection point betweenthe PMOS transistor QP16 and the NMOS transistor QN15. Between thesources of the PMOS transistors QN16 and QN17 and the voltage node Vmare connected the drain and the source of the depletion type NMOStransistor QD5, the gate of which is connected to a common-drainconnection point between the transistors QP17 and QP16. The outputsignal out1 obtained at the common-drain connection point between thetransistors QP17 and QP16 is supplied to the input terminal of thevoltage switching circuit 54D.

A circuit shown in FIG. 31C comprises an NMOS transistor QN17, a PMOStransistor QP18, and a depletion type NMOS transistor QD16. The currentpaths of the transistors QN17, QP18, and QD6 are connected in seriesbetween the ground point and the voltage node Vm, so that the outputsignal in1 of the inverter 58 is supplied to the gates of thetransistors QN17 and QP18. Furthermore, the gate of the transistor QD6is connected to a common-drain connection point between the transistorsQN17 and QP18. Accordingly, the output signal out1 obtained at thecommon-drain connection point between the transistors QN17 and QP18 issupplied to the input terminal of the voltage switching circuit 54D.

Further, a circuit shown in FIG. 31D comprises an inverter INVd, an NMOStransistor QN18, a PMOS transistor QP19, and a depletion type NMOStransistor QD7. The output signal in1 of the inverter 58 is supplied tothe input terminal of the inverter INVd and the gate of the PMOStransistor QP19. At the output of the inverter INVd is connected one endof the current path of the NMOS transistor QN18, to the gate of which isapplied the power supply voltage Vcc. Between the other end of thecurrent path of the transistor QN18 and the voltage node Vm areconnected in series the currents paths of the PMOS transistor QP19 andthe depletion type NMOS transistor QD7. The gate of the transistor QD7is connected to a connection point between the respective current pathsof the transistors QN18 and QP19. Accordingly, the output signal out1obtained at that connection point between the respective current pathsof the transistors QN18 and QP19 is supplied to the input terminal ofthe voltage switching circuit 54D.

Note here that the above-mentioned voltage switching circuit 54D mayemploy a configuration of the voltage switching circuit 54A in thecircuit shown in FIG. 7, the voltage switching circuit 54B in thecircuit shown in FIG. 11, the voltage switching circuit in the circuitshown in FIG. 13, or that shown in FIGS. 22 to 25.

The voltage of the voltage node Vm in the circuit shown in FIG. 30 maybe higher than, for example, the power supply voltage (or the powersupply voltage of the NAND gate 57 or the inverter 58) and lower thanthe highest voltage of the power supply node VPPRW (which is usuallyequal to the programming high voltage Vpp in level). When theconfiguration shown in FIG. 30 is employed, a voltage level with eitherone of the two signals input to the voltage switching circuit 54D (whichcorresponds to the signal out1 in FIG. 30) as held at the “high” levelhas a high level from the power supply voltage to the voltage Vm. Thatis, in the row decoder circuit corresponding to a non-selected block,the output of the NAND gate 57 has a “high” level, so that the signalin1 output from the inverter 58 has a “low” level, thus resulting in thesignal out1 having the Vm level. As a result, to the voltage switchingcircuit 54D is input the Vm-level signal.

A special effect can be given to a case where such circuit as shown inFIG. 30 is employed by using the voltage switching circuit 54C in thecircuit shown in FIG. 13 or such a circuit as shown in FIGS. 32 and 25as the voltage switching circuit 54D.

The following will describe this effect with reference to a case wherethe voltage switching circuit 54C in the circuit shown in FIG. 13 isused as the above-mentioned voltage switching circuit 54D. If such acircuit configuration as shown in FIG. 30 is employed, in the rowdecoder corresponding to a non-selected block, the voltage applied tothe gate of the transistor QP13 is raised from the power supply voltageto the Vm level, thus resulting in an advantage that the leakage currentthrough the transistor QP13 can be reduced. The row decoder circuit isusually provided as many as about several millions to several tens ofthousands on one chip, so that even if each row decoder circuit has asmall leakage current, the chip as a whole has a large leakage current.Therefore, the circuit configuration shown in FIG. 30 provides a largeeffect in reduction of the leakage current. This effect can be obtainednot only in the case where the voltage switching circuit in the circuitshown in FIG. 13 is applied to the voltage switching circuit 54D shownin FIG. 30 but also in a case where it is applied to the circuitconfiguration shown in FIGS. 23 and 25.

Besides, the circuit shown in FIGS. 31B to 31D employs therein thedepletion type transistors QD5 to QD7. The highest value Vm of a voltagelevel applied to those transistors QD5 to QD7 is lower than the highestvoltage level VPPRW (which is Vpp usually) applied to the depletion typeNMOS transistors QD1 to QD4. Accordingly, the gate oxide film of thetransistors WD5 to WD7 can be made thinner than that of the transistorsQD1 to QD4. Accordingly, this provides a feature that as compared to acase of a thicker gate oxide film the transistors QD5 to QD7 can bereduced in area, because the lower the highest application voltage, thelarger will a current flow through the transistors for each unit areacaused by the thinner gate oxide film, thus resulting in reduction inthe area occupied by the pattern of the transistors.

Likewise, the gate oxide film of the transistors QP14 to QP19 and QN13to QN18 can be made thinner than that of the transistors QP11 to QP13and QN13 to QN18. In this case, therefore, there is provided a featurethat the area occupied by the pattern of the transistors can be madesmaller than a case of a thinner gate oxide film.

Although the fifth embodiment has been described with reference to FIGS.30 and 31A to 31D, the present invention may be changed in a variety ofmanners; for example, the present invention is applicable to such acircuit configuration as shown in FIGS. 32 and 33A to 33D.

FIG. 32 shows a configuration example of part of the row decoder circuitin the semiconductor memory device according to a sixth embodiment ofthe present invention. A circuit shown in FIG. 32 is provided to supplythe output signal in1 of the inverter 58 and the output signal in2 ofthe NAND gate 57 in the above-mentioned circuit shown in FIG. 30 to avoltage switching circuit 54F and then supply the output signals out1and out2 of this voltage switching circuit 54F to the voltage switchingcircuit 54D.

FIGS. 33A to 33D are circuit diagrams for showing specific configurationexamples of the voltage switching circuit 54F in the above-mentionedcircuit shown in FIG. 32. To this voltage switching circuit 54F areinput the output signal in1 of the inverter 58 an the output signal in2of the NAND gate 57, so that in the circuit shown in FIGS. 33A and 33B,when the signal in1 is at a “high” level (the signal in2 is at a “low”level) the signal out1 is set to 0V and the signal out2 is set to the Vmlevel, and when the signal in1 is at a “low” level (the signal in2 is ata “high” level) the signal out1 is set to the Vm level and the signalout2 is set to 0V. Moreover, in the circuit shown in FIGS. 33C and 33D,when the signal in1 is at a “high” level (the signal in2 is at a “low”level) the signal out1 is set to 0V and the signal out2 is set to theVcc level, and when the signal in1 is at a “low” level (the signal in2is at a “high” level) the signal out1 is set to the Vm level and thesignal out2 is set to 0V.

A circuit shown in FIG. 33A comprises NMOS transistors QN13 and QN14 andPMOS transistors QP14 and QP15. The output signal in1 of the inverter 58is supplied to the gate of the NMOS transistor QN14 and the outputsignal in2 of the NAND gate 57, to the gate of the NMOS transistor QN13.The sources of the NMOS transistors QN13 and QN14 are connected to theground point and between their drains and the voltage node Vm areconnected the drains and sources of the PMOS transistors QP14 and QP15.The gate of the PMOS transistor QP14 is connected to a common-drainconnection point between the PMOS transistor QP15 and the NMOStransistor QN14 and the gate of the PMOS transistor QP15, to acommon-drain connection point between the PMOS transistor QP14 and theNMOS transistor QN13. Accordingly, the output signal out1 obtained atthe common-drain connection point between the transistors QP15 and QN14and the output signal out2 obtained at the common-drain connection pointbetween the transistors QP14 and QN13 are supplied to the respectiveinput terminals of the voltage switching circuit 54D.

Furthermore, a circuit shown in FIG. 33B comprises NMOS transistors QN15and QN16, PMOS transistors QP16 and QP17, and a depletion type NMOStransistor QD5. The output signal in1 of the inverter 58 is supplied tothe gate of the NMOS transistor QN16 and the output signal in2 of theNAND gate 57, to the gate of the NMOS transistor QN15. The source of theNMOS transistors QN15 and QN16 are connected to the ground point andtheir drains are connected with the drains of the PMOS transistors QP16and QP17 respectively. The gate of the PMOS transistor QP16 is connectedto a common-drain connection point between the PMOS transistor QP17 andthe NMOS transistor QN16 and the gate of the PMOS transistor QP17, to acommon-drain connection point between the PMOS transistor QP16 and theNMOS transistor QN15. Between the sources of the PMOS transistors QP16and QP17 and the voltage node Vm are connected the drain and source ofthe depletion type NMOS transistor QD5, the gate of which is connectedto the common-drain connection point between the transistors QP17 andQN16. Accordingly, the output signal out1 obtained at the common-drainconnection point between the transistors QP17 and QN16 and the outputsignal out2 obtained at the common-drain connection point between thetransistors QP16 and QN15 are supplied to the respective input terminalsof the voltage switching circuit 54D.

A circuit shown in FIG. 33C comprises an inverter INVe, an NMOStransistor QN17, a PMOS transistor QP18, and a depletion type NMOStransistor QD6. The current paths of the transistors QN17, QP18, and QD6are connected in series between the ground point and the voltage nodeVm, so that the output signal in1 of the inverter 58 is supplied to thegates of the transistors QN17 and QP18. Moreover, the gate of thetransistor QD6 is connected to a common-drain connection point betweenthe transistors QN17 and QP18. Further, the output signal in2 of theNAND gate 57 is supplied to the input terminal of the inverter INVe.Accordingly, the output signal out1 obtained at the common-drainconnection point between the transistors QN17 and QP18 and the outputsignal out2 output from the output terminal of the inverter INVe aresupplied to the respective input terminals of the voltage switchingcircuit 54D.

Further, a circuit shown n FIG. 33D comprises an inverter INVf, an NMOStransistor QN18, a PMOS transistor QP19, and a depletion type NMOStransistor QD7. The output signal in1 of the inverter 58 is supplied tothe gate of the PMOS transistor QP19 and the output signal in2 of theNAND gate 57 is supplied to one end of the current path of the NMOStransistor QN18 and the input terminal of the inverter INVf. The powersupply voltage Vcc is applied to the gate of the transistor QN18,between the other end of the current path of which and the voltage nodeVm are connected in series the current paths of the PMOS transistor QP19and the depletion type NMOS transistor QD7. The gate of the transistorQD7 is connected to a connection point between the current paths of thetransistors QN18 and QP19. Accordingly, the output signal obtained atthe common-drain connection point between the transistors QN18 and QP19and the output signal out2 output from the output terminal of theinverter INVf are supplied to the respective input terminals of thevoltage switching circuit 54D.

Such a circuit configuration as shown above in FIGS. 32 and 33A to 33Dalso has almost the same effect hence essentially the same actions andeffects as those by the circuit configuration mentioned above withreference to FIGS. 30 and 31A to 31D.

Since, in such a circuit as shown in FIGS. 31A and 33A, the voltageVPPRW is applied to the n-well region, in which the PMOS transistorsQP14 to QP19 are formed in the above-mentioned circuit shown in FIGS. 32and 33A to 33D, commonly over a plurality of the relevant blocks, theabove-mentioned configuration shown in FIG. 12A is suited. In such aconfiguration as shown in FIGS. 31B to 31D and 33B to 33D, on the otherhand, the n-well voltage is not common, so that the configuration shownin FIGS. 12B, 18 to 20, 21A to 21E, 26 to 28, and 29A and 29B is suited.

FIGS. 34 and 35 are circuit diagrams for explaining the semiconductormemory device according to the other embodiments of the presentinvention, specifically showing an extracted circuit portion forsupplying the voltage VPPRW to the voltage switching circuits 54 (54A to54D) in the above-mentioned first through fifth embodiments. Thosecircuits are provided for switching the power supply node VPPRW betweena stand-by state and an active state according to the Active signal.

That is, the circuit portion shown in FIG. 34 comprises a high-voltagegenerating circuit 60, an inverter 61, a PMOS transistor QP20, and adepletion type NMOS transistor QD8. At an output terminal of theabove-mentioned high-voltage generating circuit 60 is connected thepower supply node VPPRW of the voltage switching circuit 54, betweenwhich node VPPRW and the power supply voltage Vcc are connected inseries the current paths of the transistors QD8 and QP20. The gate ofthe PMOS transistor QP20 is supplied with the Active signal via theinverter 61 and the gate of the depletion type NMOS transistor QD8, withthe above-mentioned Active signal.

In the above-mentioned configuration, the Active signal is at 0V in thestand-by state and at Vcc in the active state and is generated on thebasis of the Chip Enable signal input from, for example the /CE pin.Furthermore, the above-mentioned high-voltage generating circuit 60 isconfigured so as to be inoperative in the stand-by state.

Since the above-mentioned Active signal is at 0V in the stand-by state,the transistor QP20 is turned OFF and therefore the power supply nodeVPPRW enters a floating state. When the Active signal is set to Vcc inthe active state, on the other hand, the transistor QP20 is turned ONand therefore the node VPPRW is charged up to the power supply voltageVcc. Afterward, the high-voltage generating circuit 60 sets the nodeVPPRW to a high voltage and, at the same time, the Active signal is setto 0V, to thereby turn OFF the transistor QD8, thus releasing the powersupply node VPPRW from the power supply Vcc.

Thus, it is possible to suppress the occurrence of a leakage current inthe stand-by state and, in the active state (where speedy charge-up toVcc is possible), accelerate the charging of the power supply node VPPRWto the high voltage.

The circuit portion shown in FIG. 35, on the other hand, comprises thehigh-voltage generating circuit 60 and a depletion type NMOS transistorQD9. At the output terminal of the high-voltage generating circuit 60 isconnected the power supply node VPPRW of the voltage switching circuit54, between which node VPPRW and the power supply Vcc is connected thecurrent path of the transistor QD9. Accordingly, the gate of theabove-mentioned depletion type NMOS transistor QD9 is supplied with theActive signal.

Such a configuration operates in almost the same manner as theabove-mentioned circuit shown in FIG. 34 and gives almost the sameactions and effects.

Although the present invention has been described with reference to theembodiments, the present invention is not limited to them but may bechanged in various manners.

For example, although the above-mentioned embodiments of the presentinvention have been described in such an example that a voltage of 0V orhigher is applied to a selected word line, the polarity may be reversed,that is, a voltage of 0V or lower may be applied to a selected wordline, in which case the present invention is applicable in such a mannerthat the polarity is reversed, i.e. the NMOS transistor is changed to aPMOS one in the above-mentioned voltage switching circuit or, in thisvoltage switching circuit, the PMOS transistor is changed to an NMOS oneand, at the same time, the transistor directly connected to the wordline is changed from an NMOS type to a PMOS type.

Furthermore, although the above-mentioned embodiments of the presentinvention have been described in an example where the present inventionis applied to the row decoder, any other configuration or connectionrelationship for voltage application may be used of the voltageswitching circuit and the word line-connected transistors in theabove-mentioned embodiments.

In addition, although the above-mentioned embodiments have beendescribed in an example that eight memory cells are connected in seriesin each NAND cell, the number of these memory cells is not limited toeight but may be, for example, two, four, 16, 32, or 64, to which casesthe present invention is also applicable. Moreover, the presentinvention is applicable to a case where only one memory cell is presentwith the select gate transistors. In addition, although theabove-mentioned embodiments have been described in an example of a NANDcell-type EEPROM, the present invention is not limited to such a casebut may be applicable also to such a case of any other devices, forexample, NOR cell-type EEPROM, DINOR cell-type EEPROM, AND cell-typeEEPROM, or NOR cell-type EEPROM provided with a select transistor.

FIG. 36 shows an equivalent circuit diagram of a memory cell array in aNOR cell-type EEPROM. This memory cell array includes NOR cells Mjo toMj+2m at the intersections of word lines WLj, WLj+1, WLj+2, . . . andbit lines BL0, BL1, . . . , BLm respectively in such a configurationthat the control gates of these NOR cells Mj0 to Mj+2m are connected tothe word lines WLj, WLj+1, WLj+2, . . . in the rows and the drains areconnected to the bit lines BL0, BL1, . . . , BLm in the columnsrespectively and the sources are commonly connected to the source lineSL.

Furthermore, FIG. 37 shows an equivalent circuit diagram of a memorycell array in a DINOR cell-type EEPROM. In the DINOR cell-type memorycell array, one DINOR cell is provided for each of the main bit linesD0, D1, . . . , Dn. Each DINOR cell comprises select gate transistorsSQ0, SQ1, . . . , SQn and memory cells M00 to M31 n in such aconfiguration that the drains of these select gate transistors SQ0, SQ1,. . . , SQn are connected to the bit lines D0, D1, . . . , Dnrespectively, the gates are commonly connected to the select gate lineST, and the sources are connected to the local bit lines LB0, LB1, . . ., LBn respectively. The drains of those memory cells M00 to M31 n areconnected to the local bit lines LB0, LB1, . . . , LBn in the rows, thecontrol gates are connected to the word lines W0 to W31 in the columns,and the sources are commonly connected to the source line SL.

FIG. 38 shows an equivalent circuit diagram of the memory cell array inan AND cell-type EEPROM. In the AND cell-type memory array, one AND cellis provided for each of the main bit lines D0, D1, . . . , Dn. Each ANDcell comprises first select gate transistors SQ10, SQ11, . . . , SQ1 n,memory cells M00-M31 n, and second select gate transistors SQ20, SQ21, .. . , SQ21 n in such a configuration that the drains of these firstselect gate transistors SQ10, SQ11, . . . , SQ1 n are connected to themain bit lines D0, D1, . . . , Dn respectively, the gates are commonlyconnected to the first select gate line ST1, and the sources areconnected to the local bit lines LB0, LB1, . . . , LBn respectively. Thedrains of the memory cells M00 to M31 n are connected to the local bitlines LB0, LB1, . . . , LBn in the rows respectively, the control gatesare connected to the word lines W0 to W31 in the columns respectively,and the sources are connected to the local source lines LS0, LS1, . . ., LSn respectively. The drains of the second select gate transistorsSQ20, SQ21, . . . , SQ2 n are connected to the local source lines LS0,LS1, . . . , LSn respectively, the gates are connected to the secondselect gate line ST2, and the sources are commonly connected to the mainsource line MSL.

Further, FIG. 39 shows an equivalent circuit diagram of the memory cellarray in a NOR cell-type EEPROM provided with a select transistor. Inthis memory cell array, a plurality of memory cells MC each comprising aselect transistor SQ and a memory cell transistor M is arranged in amatrix. The drains of all the select transistors SQ in each column areconnected to each of bit lines BL0, BL1, . . . , BLn, the gates thereofin each row are connected to each of the select gate lines ST, and thesources thereof are connected to the drains of the corresponding memorycell transistors M. The control gates of all the memory cell transistorsM in each row are connected to each of the word lines WL and the sourcesthereof are commonly connected to the source line SL.

For details of the DINOR cell-type EEPROM, see “H. Onoda et al., IEDMTech. Digest, 1992, pp. 599-602” and for details of the above-mentionedAND cell-type EEPROM, see “H. Kume et al., IEDM Tech. Digest, 1992, pp991-993”.

Although the embodiments of the present invention have been describedwith reference to an example of a nonvolatile memory device capable ofelectrical rewriting, the present invention is applicable also to othertypes of devices, e.g., other types of nonvolatile memory devices,DRAMs, SRAMs, etc.

Although the present invention has been described with reference to itsembodiments, the present invention is not limited to them but may bechanged in a variety of manners within the gist thereof. Further, theabove-mentioned embodiments include a variety of steps of the presentinvention, so that by appropriately combining some of the plurality ofdisclosed component requirements, a variety of inventions can beextracted. For example, even if some of all the component requirementsdisclosed in the embodiments are deleted, at least one of theabove-mentioned problems to be solved by the present invention can besolved, so that a configuration given as a result of this deletion canbe extracted as far as at least one of the above-mentioned effects isobtained.

As mentioned above, by the present invention, it is possible tointernally provide a row decoder with a voltage switching circuitincluding PMOS transistors to thereby set the gate of each NMOStransistor to a high voltage without providing a pump circuit, even in acase where only one NMOS transistor is connected to each word line inthe row decoder circuit.

Therefore, it is possible to apply a high voltage to the word linewithout a potential drop and also to obtain a semiconductor memorydevice having a reduced area of the pattern of the row decoder circuit.

Furthermore, it is possible to realize the row decoder circuit havingsuch a small pattern area, thus obtaining a semiconductor memory devicecapable of realizing an inexpensive and highly reliable chip.

Further, it is possible to apply a high voltage to the word line withouta potential drop, thus obtaining a semiconductor memory device capableof realizing an appropriate data programming operation.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A semiconductor memory device comprising: a memory cell array inwhich memory cells are arranged in a matrix including a plurality ofword lines and a plurality of bit lines; a plurality of blocks, each ofthe blocks including memory cells connected to a plurality of wordlines; a plurality of row decoder circuits selecting a first word linein the memory cell array and applying a voltage to the first word line,one of the row decoder circuits being provided for a corresponding oneof the blocks; a plurality of first transistors having a firstconductivity type, a source or a drain of each of the first transistorsbeing connected to a corresponding one of the word lines, two or more ofthe first transistors being included in each of the row decodercircuits; a plurality of second transistors having a second conductivitytype opposite to the first conductivity type, a drain of the secondtransistor being connected to a gate of the first transistor, at leastone of the second transistors being included in each of the row decodercircuits; and a plurality of well regions in each of which the secondtransistor is formed, the well regions having the first conductivitytype, one of the well regions being formed for a corresponding one ofthe blocks; wherein when at least one word line in a selected block isset to a first voltage which is higher than a power supply voltage, thesecond transistor applies a second voltage to the gate of the firsttransistor, the second voltage is higher than the first voltage, and afirst well region corresponding to one block is separated from wellregions corresponding to the other blocks.